1. Field of the Invention
The invention relates to an optoelectronic module, which can be employed in particular in optoelectronic travel, angle and rotational measuring instruments or other optoelectronic devices.
2. Description of the Related Art
In the journal xe2x80x9cFandMxe2x80x9d, No. 10 (1996), Vol. 104, pages 752-756, an emitter-receiver module is disclosed. An LED is disposed on a photodiode array chip, which is connected via gold bumps to conductor tracks on a transparent glass plate in what is known as flip-chip technology. The intermediate space between the chip and the glass substrate is filled with an underfiller for the sake of mechanical stabilization. This arrangement is intended to project light onto a scale by means of the LED and to detect the reflected light by the photodiodes. It is disadvantageous, however, that the underfiller is a very good light guide, which guides a large portion of the light in the underfiller, which has been projected by the LED, to the photodiodes. Portions of the light are diverted to the photodiodes by scattering in the underfiller and reflection at the boundary faces of the underfiller and the glass substrate, and further portions are projected directly at the edges of the LED onto the receiver surfaces of the optic chip. As a consequence, the proportion of useful light to parasitic or unwanted light striking the photodiodes is unfavorable.
From German Patent Disclosure DE 197 20 300 A, a chip- in-chip implantation of a gallium arsenide LED chip in a silicon-PIN-diode receiver matrix is known. Once again, there can be a considerable proportion of scattered light, which strikes the diode receiver matrix directly without taking the desired course, for instance to a scale having an optical graduation. As a result, on the one hand the useful signal proportion is reduced considerably, and on the other the photodiodes are already modulated with a considerable proportion of direct light. In such flip-chip assemblies, it is also conventional and for applications indispensable, for the sake of mechanical stability and surface passivation, that an optical underfiller be placed between the chip surfaces and the glass substrate plate. The underfiller does provide high mechanical strength and chemical resistance, but it causes an even larger proportion of light to be coupled directly to the photodiode surfaces. Once again, the optoelectronic efficiency is markedly worse as a result.
With this as the point of departure, an object and advantage of the present invention is to create an optoelectronic module in which the proportion of useful light to parasitic or unwanted light is improved.
The above object and advantage is attained by an optoelectronic module including a transparent substrate that carries a conductor track, an optoelectronic chip having an optoelectronic sensor and/or emitter for light disposed on the substrate and via a contacting element the chip is connected to the conductor track and kept spaced apart from the transparent substrate. An opaque light blocking element, disposed between the substrate and the chip, that shields the sensor from lateral incident light and/or lateral light opposite the emitter.
The optoelectronic module of the present invention has a transparent substrate that carries conductor tracks. This substrate may be in platelike form. Glass and/or plastic can be considered in particular as the material for the substrate.
An optoelectronic chip with at least one sensor and/or emitter for light is also present, which is disposed with the sensor and/or emitter oriented toward the substrate on the substrate. The sensor and/or emitter can be embodied in one face of the chip. However, it can also be an additional component that is mounted on the chip.
The chip is connected to the conductor tracks and kept at a distance from the transparent substrate via contacting elements. The contacting elements serve the purpose of both mechanical and electrical connection of the chip to the substrate or to the conductor tracks disposed on it. Gold bumps or similar contacting elements can be considered in particular as the contacting elements. The known flip-chip technology can be employed.
In the optoelectronic module, an underfiller is preferably disposed between the chip and the transparent substrate. The underfiller can be transparent, especially if it covers an optoelectronic sensor and/or emitter. The underfiller may involve an epoxy resin, silicone, or a similar hardening plastic material. An underfiller is indeed preferred but is not obligatory.
Finally, in the intermediate space between the chip and the transparent substrate, an opaque light blocking element is disposed, which more or less shields off the sensor from lateral incident light and/or lateral light projected by the emitter. Lateral denotes means an incidence of light or projection of light from or in a direction that is inclined to a vertical axis or line through the chip. This means, for instance, an incident light that does not originate directly at a specific external object but instead is due to scattering or reflection, or it can also be direct radiation from some other object. This parasitic or unwanted light can also originate in a light emitter integrated with the module. It can also be a light projection that is not aimed directly at a different object. As a consequence, in the module of the present invention, the proportion of parasitic or unwanted light striking the sensor or transmitted by the emitter is at least reduced considerably, and on the other hand, the proportion of useful light is increased.
The present invention also encompasses an only partial suppression of parasitic or unwanted light by the light blocking element. It is also within the scope of the present invention that the light blocking element is not ideally opaque, and the substrate and optionally the underfiller are not ideally transparent. Within the scope of the present invention, an opacity or transparency may exist with regard to only certain light wavelengths or light length ranges of a light source with which the optoelectronic module cooperates. The decisive factor is that a considerable suppression of parasitic or unwanted light in favor of the useful light is attained for at least a certain light wavelength.
The module may be purely a receiver module that cooperates with an external artificial or natural light source. In that case, the light blocking element especially suppresses the interfering influence of scattered and extraneous light. However, it can also be purely an emitter module that especially effectively transmits light to some external object. It can also be an emitter-receiver module, in which an emitter is disposed on the chip, and the light blocking element is disposed between the emitter and the sensor. The emitter can in particular be an LED. The light blocking element prevents both optical crosstalk from the emitter to the sensor and the incidence of extraneous light onto the sensor.
Especially if underfillers or some similar optically transparent potting compound is employed, the parasitic or unwanted light due to scattering and reflection is minimized in the module, and thermomechanical stresses in the overall structure can also be kept very low. Such stresses can be due in particular to the different coefficients of thermal expansion of the materials. To adapt the coefficients of expansion toward that of gold bumps, underfillers are often filled with finely ground quartz, but this in turn increases the proportion of scattered light. The present invention makes it easier to use such underfillers and ,thus, to reduce thermomechanical stresses.
The light blocking element is preferably of a conformable material that conforms to the chip and/or to the transparent substrate. This counteracts a passage of light between the light blocking element and the chip or substrate. For production reasons, however, the light blocking element can be solidly joined to the chip and/or the transparent substrate for this purpose. Thus, the light blocking element can include a commercially available silicone rubber or some other injection moldable material. For economic production, this material can already be applied to the wafer of the chip with a dispenser before the wafer is sawn apart. Another economical method uses a printable material, which is applied as a light blocking element by screen printing, for instance. In this way, light blocking elements can also be printed on in the wafer grouping. Naturally, it is also conceivable to apply the light blocking element to the transparent substrate and then to mount the chip.
The light blocking element is preferably elastically deformable. To that end, it can comprise silicone or some other elastically deformable material. It can be disposed, elastically prestressed, between the transparent substrate and the chip. The elastic light blocking element is capable of compensating for tolerances in the spacing between the transparent substrate and the optoelectronic chip that are due in particular to the technology of the connecting elements. In gold bumps, for instance, differences in spacing of approximately 20% are entirely normal. The elasticity assures a good lightproof contact with both the transparent substrate and the chip that prevents a passage of parasitic or unwanted light through them.
Precisely in the case of an elastic light blocking element, the bonding wires and/or leads needed can be passed between contacting faces of the light blocking element on the chip and/or on the transparent substrate. These bonding wires and/or conductor tracks can lead to an emitter and/or to a sensor. The bonding wires of an emitter can, however, also be passed through the light blocking element. The elastic light blocking element can also compensate for tolerances in the amount of underfiller employed, if the underfiller is positively displaced laterally in the bonding of the chip and the substrate.
The light blocking element can have various shapes. The suppression of parasitic or unwanted light is especially advantageous if the light blocking element surrounds the sensor and/or the emitter. In the case of an emitter-receiver module with a central light emitter and sensors distributed around it, for instance, the light blocking element can be disposed around the emitter. Especially in this case, it can be circular-annular in shape. It can also be embodied in matrix form in accordance with the disposition of a plurality of sensors on one chip and can surround a plurality of sensors.
The light blocking element can be; manufactured as a micromolded part. It can have specially designed channels that enable the underfiller to be introduced after the chip has been mounted on the substrate. Special laminations disposed in meandering fashion in the channels allow the underfiller to flow through, on the hand, and on the other they assure maximum lightproofness.
The inside face of the light blocking element can also be embodied such that it contributes to a better light yield from the light source. To that end, it can have a spherical, a spherical or planar form. As a result, an otherwise ineffective edge radiation from an LED can be utilized by targeted reflection from the inside face of the light blocking element.
The module can be used in particular in an optoelectronic instrument for measuring travel, angle or rotation. To that end, the emitter can be disposed either on the module or outside the module. The transparent substrate can then have a scanning grating for scanning of a scale.
The invention will be described in further detail below in terms of exemplary embodiments.